Catalytic process for the decomposition of perfluoroalkanes

ABSTRACT

A process and composition for transforming perfluoroalkanes in the presence of an oxidizing agent and water at temperatures between about 400 to 1,000° C. Aluminum oxide is the primary agent for effecting this transformation. Additions of between 0.1 to 50% by weight of other components such as barium calcium, phosphorus, cerium, chromium, cobalt, iron, lanthanum, magnesium, nickel, silicon, titanium, yttrium or zirconium aid in extending the useful life of the catalyst. A preferred catalyst composition includes aluminum oxide with additions of cobalt and one or more of the elements of cerium, titanium or zirconium.

This application is a division of Ser. No. 08/662,129 filed Jun. 12,1996 now U.S. Pat. No. 6,069,291.

TECHNICAL FIELD

The present invention relates generally to a catalytic process andparticularly to the treatment of perfluoroalkanes. Perfluoroalkanesrepresent a specific group of halogen-containing compounds consisting ofstraight, branched and cyclic alkanes that are composed of only carbonand fluorine atoms.

BACKGROUND ART

Perfluoroalkanes refer to a specific group of halogen-containingcompounds that are composed of only carbon and fluorine atoms and do notpossess double or triple bonds. Perfluoroalkanes differ from, forexample, chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's)and hydrofluorocarbons (HFC's) in that perfluoroalkanes do not containhydrogen, chlorine or heteroatoms other than fluorine. Perfluoroalkanesare released to the environment during certain industrial processes,such as electrolytic aluminum smelting for example, as by-productsduring the manufacture of tetrafluoroethylene, and during semiconductormanufacturing processes. Examples of perfluoroalkanes include carbontetrafluoride (CF₄), hexafluoroethane (C₂F₆), octafluoropropane (C₃F₈),octafluorocyclobutane (C₄F₈) and decafluoroisobutane (C₄F₁₀)Perfluoroalkanes represent some of the most stable compounds known(Kiplinger et al. Chem. Rev. p. 373 (1994). The stability ofperfluoroalkanes makes these compounds difficult to decompose or convertto useful products, such as for example the conversion ofperfluoroalkanes to perfluoroalkenes. Also, this highly stablecharacteristic make perfluoroalkanes released into the atmosphereundesirable because of their contribution to global warming effects.

A number of catalysts and catalytic processes have been reported for thedecomposition of halogen-containing organic compounds. A review of theliterature reveals that the majority of these catalysts and catalyticprocesses focus on the decomposition of chlorine-containing compounds,or the destruction of organic compounds which contain only chlorine andfluorine. Bond and Sadeghi, in an article entitled “CatalyzedDestruction of Chlorinated Hydrocarbons”, J.Appl. Chem. Biotechnol, p.241 (1975), report the destruction of chlorinated hydrocarbons over aplatinum catalyst supported on high surface area alumina.

Karmaker and Green, in an article entitled “An investigation of CFC12(Ccl₂F₂) decomposition on TiO₂ Catalyst,” J. Catal, p. 394 (1995),report the use of a TiO₂ catalyst to destroy CFC12 at reactiontemperatures between 200 and 400° C. in streams of humid air.

Bickel et al, in an article entitled “Catalytic Destruction ofChlorofluorocarbons and Toxic Chlorinated Hydrocarbons”, Appl. CatalB:Env. p. 141 (1994), report the use of a platinum catalyst supported onphosphate-doped zirconium oxide for the destruction of CFC113(Cl₂FCCClF₂) in air streams. The catalyst was able to achieve greaterthan 95% destruction of CFC113 at reaction temperature of 500° C. forapproximately 300 hours of continuous operation.

Fan and Yates, in an article entitled “Infrared Study of the Oxidationof Hexafluoropropene on TiO₂ ,” J. Phys. Chem., p. 1061 (1994), reportthe destruction of a perfluoroalkene over TiO₂. Perfluoroalkenes differfrom perfluoroalkanes in that they contain a carbon-carbon double bond.Although the catalyst was able to readily destroy hexafluoropropylene(C₃F₆), the loss of titanium, as TiF₄, was evident. The formation ofTiF₄ would undoubtedly lead to deactivation of the catalyst.

Farris et al, in an article entitled “Deactivation of a Pt/Al₂O₃Catalyst During the Oxidation of Hexafluoropropylene,” Catal. Today, p.501 (1992), report the destruction of hexafluoropropylene over aplatinum catalyst supported on a high surface area alumina carrier.Although the catalyst could readily destroy hexafluoropropylene atreaction temperatures between 300 and 400° C., deactivation of thecatalyst, resulting from the transformation of aluminum oxide toaluminum trifluoride, was severe.

Campbell and Rossin, in a paper entitled “Catalytic Oxidation ofPerfluorocyclobutene over a Pt/TiO₂ Catalyst,” presented at the 14th N.Am. Catal. Soc. Meeting (1995), reported the use of a platinum catalystsupported on high surface area TiO₂ carrier to destroyperfluorocyclobutene (C₄F₆) at reaction temperatures between 320 and410° C. The authors note than even at a reaction temperature of 550° C.,no conversion of perfluorocyclobutane (C₄F₈), a perfluoroalkane, couldbe achieved using the Pt/TiO₂ catalyst. Results presented in this studydemonstrate that perfluoroalkanes are significantly more difficult totransform than perfluoroalkenes.

Nagata et al, in a paper entitled “Catalytic Oxidative Decomposition ofChlorofluorocarbons (CFC's) in the Presence of Hydrocarbons”, Appl.Catal. B:Env., p. 23 (1994), report the destruction of 1,1,2-trichloro1,2,2-trifluoroethane (CFC113), 1,2 dichloro 1,1,2,2-tetrafluoroethane(CFC114) and chloropentafluoroethane (CFC115) in the presence ofhydrocarbons using a γ-alumina catalyst impregnated with vanadium,molybdenum, tungsten and platinum. The decomposition of the CFC's becamemore difficult as the number of carbon atoms in the CFC moleculedecreased. However, results indicate that as the number of chlorineatoms in the molecule are decreased by replacement with fluorine, thecompounds become increasingly more difficult to decompose.

Burdeniue and Crabtree, in an article entitled “Mineralization ofChlorofluorocarbons and Aromatization of Saturated Fluorocarbons by aConvenient Thermal Process”, Science, p. 340 (1996), report thetransformation of cyclic perfluoroalkanes to perfluoroarenes via contactwith sodium oxalate to yield sodium fluoride as a reaction product. Bothreactions, however, are slow and non-catalytic, since sodium oxalate isstoichiometrically consumed (via transformation into NaF) during thecourse of the reaction.

This process would not be able to destroy perfluoroalkanes present instreams of air, since the oxygen and/or moisture in the air wouldreadily convert the sodium oxalate to sodium oxide.

SUMMARY OF INVENTION

The present invention is directed to processes for the transformation ofperfluoroalkanes and for catalytic compositions used therein. Moreparticularly, the present invention is directed to a process for thetransformation of perfluoroalkanes comprising contacting theperfluoroalkanes with aluminum oxide. According to one embodiment, theperfluoroalkane is contacted with aluminum oxide at a temperatureranging from about 400° C. to about 1000° C. According to a furtherembodiment of the invention, the process for the transformation of aperfluoroalkane comprises contacting the perfluoroalkane with aluminumoxide at a temperature ranging from about 550° C. to about 800° C.

The present invention is also directed to a process for thetransformation of perfluoroalkanes comprising contacting theperfluoroalkane with aluminum oxide wherein said aluminum oxide isstabilized, for example, with an element selected from the groupconsisting of barium, calcium, cerium, chromium, cobalt, iron,lanthanum, phosphorus, magnesium, nickel, silicon, titanium, yttrium,and zirconium. In a further embodiment, the aluminum oxide may bestabilized with molybdenum; tungsten, and vanadium.

According to another embodiment of the present invention, the process oftransforming a perfluoroalkane comprises contacting the perfluoroalkanewith aluminum oxide in the presence of water and an oxidizing agent.

According to a further embodiment of the invention, the processcomprises contacting the perfluoroalkane with a composition comprisingaluminum oxide, cobalt, for example, less than 50% by weight cobalt,and, for example, less than 50% by weight of at least one elementselected from the group consisting of cerium, titanium, and zirconium.

According to another embodiment of the present invention, the inventionis directed to a composition for the transformation of perfluoroalkanescomprising aluminum oxide, and at least one element selected from thegroup consisting of barium, calcium, cerium, chromium, cobalt, iron,lanthanum, magnesium, molybdenum, nickel, tin, titanium, tungsten,vanadium, yttrium, and zirconium.

According to another embodiment of the present invention, the inventionis directed to a composition for the transformation of a perfluoroalkanecomprising aluminum oxide, cobalt, for example, less than 50% by weight,and at least one element selected from the group consisting of cerium,titanium, and zirconium, for example, less than 50% by weight of one ofsaid elements.

According to a still further embodiment of the present invention, theinvention is directed to a composition for the transformation of aperfluoroalkane comprising aluminum oxide. In one embodiment of thepresent invention, the aluminum oxide may be stabilized with, forexample, an element selected from the group consisting of barium,calcium, cerium, chromium, cobalt, iron, lanthanum, phosphorus,magnesium, nickel, silicon, titanium, yttrium, and zirconium. Accordingto a still further embodiment, the aluminum oxide may be stabilized withan element selected from the group consisting of molybdenum, tungsten,and vanadium.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates generally to a novel catalytic process forthe transformation of perfluoroalkanes, such as for example, thosevented to the atmosphere during chemical process operations. Examples ofthese processes include perfluoroalkanes generated during electrolyticaluminum smelting, tetrafluoroethylene manufacture, and duringsemiconductor manufacture. The process according to the presentinvention employs aluminum oxide as a catalyst, where the aluminum oxidemay be of several phases, such as for example gamma, alpha, delta, kappaand theta, or a combination of phases, with the gamma phase being thepreferred phase of aluminum oxide. While testing has shown aluminumoxide will readily destroy perfluoroalkanes at reaction temperaturesbetween 400 and 1,000° C., the useful life-time of the catalyst appearsto be limited due to deactivation resulting from an interaction betweenfluorine atoms liberated during the destruction of the perfluoroalkaneand elemental aluminum which comprises the catalyst.

A preferred catalyst composition comprises aluminum oxide with theaddition of between 0.01 and 50% of one or more elements selected from agroup which include barium, calcium, cerium, chromium, cobalt, iron,lanthanum, phosphorus, magnesium, nickel, silicon, titanium, yttrium andzirconium. A more preferred catalyst consists of aluminum oxidecontaining cerium, titanium or zirconium, and cobalt. Other usefulcomponents which may be added to the aluminum oxide include molybdenum,tungsten or vanadium.

The catalyst may be used in any configuration or size which sufficientlyexposes the catalyst to the gas stream being treated. The catalystcomposition may be configured in many typical and well-known forms, suchas for example, pellets, granules, rings, spheres or cylinders.Alternatively, the catalyst composition may take the form of a coatingon an inert carrier, such as ceramic foams, spheres or monoliths. Themonolithic form may be preferred when it is desired to reduce thepressure drop through the system or minimize attrition or dusting.

The additional components may be dispersed onto the aluminum oxide bycontacting the aluminum oxide with an aqueous or non-aqueous solutioncontaining one or more of these components. Once the impregnation stepis completed, the resulting material may be dried and/or calcined. Iftwo or more additional components are to be employed, a preferred methodof catalyst preparation may involve sequentially impregnating thealuminum oxide with a solution containing one or more of these addedcomponents followed by drying and/or calcining the resulting material.Once this step is completed, the resulting material may be impregnatedwith a solution containing the same or other of these additionalcomponents, followed again by drying and calcining the resultingmaterial. These steps may be repeated until all the additionalcomponents have been added in the amount desired. In all cases, thesolution containing the additional components may be aqueous ornon-aqueous.

Alternatively, the additional components may be added during thepreparation of the aluminum oxide. In this instance, the catalyst isprepared by slurrying pseudoboehmite aluminum oxide (Al₂O₃.1.5H₂O) in anaqueous or non-aqueous liquid with an appropriate mixing device andadjusting the pH to between 1.0 and 6.0 using an appropriate acid, suchas nitric, formic or acetic. Once mixed, one or more additionalcomponents may be added to the slurry. These additional components maybe added as solid metal salts, such as nitrates, acetates, oxalates,chlorides, halides, etc., or may be added as small metal or metal oxideparticles, such as for example cerium oxide. Once mixed, the slurry maybe aged, if desired, or used directly in the manufacture of beads,particles, spheres, rings, etc., or used to coat an inert ceramicsubstrate, such as a monolith. Following manufacture or coating of theinert ceramic substrate, the resulting material must be calcined at atemperature between 350 and 900° C., with the preferred calcinationtemperature being between about 500 and 600° C.

It should be noted that the additional elements added to the aluminumoxide should be highly dispersed throughout the particular configurationused.

If one wishes to manufacture catalyst particles, for example, theresulting slurry described above is first dried, then calcined at atemperature sufficient to form the desired aluminum oxide phase, such asbetween 500 and 600° C. if one wishes to form the gamma phase ofaluminum oxide. Once calcined, the resulting material may be crushed andsieved to the desired mesh size range.

Alternatively, if the monolithic form of the catalyst is desired, themonolithic form may be prepared, for example, by dipping the monolithicsubstrate into a pseudoboehmite slurry, or a pseudoboehmite slurrycontaining one or more additional components. Excess slurry may beremoved from the channels of the monolithic substrate using an air knifeaccording to procedures well known to one skilled in the art. Thecatalyst-coated monolith is then dried and calcined at a temperaturesuitable to achieve the desired form of aluminum oxide. The wash coatingprocedure can be repeated as often as required until the desired loadingof catalyst is achieved. It is desirable that the amount of the catalystcomposition coated onto the monolith be in the range of about 25 toabout 350 g/liter.

The novel catalytic process of the present invention preferably involvespassing a gas stream containing one or more perfluoroalkanes, anoxidizing agent, such as air, and water vapor through a catalyst bedcontaining a catalyst composition as described herein and heated to thedesired operating temperature. The flow rates through the system shouldbe sufficient to allow for greater than at least 80% and preferablygreater than 90% so destruction of the perfluoroalkane(s) present in thestream. Thus, the gas hourly spaced velocity (GHSV) can varysignificantly over the range of about 500 to about 300,000 h⁻¹, andpreferably in the range of about 1,000 to about 20,000 h⁻¹. The processdescribed herein may be operated at temperatures between about 400° C.to about 1,000° C., with the preferred temperature range between about500 and 800° C.

The process described according to the present invention is alsoapplicable to the injection of gaseous or liquid phase perfluoroalkanesor mixtures of perfluoroalkanes into a gas stream, including anoxidizing agent, such as air for example, and water. The gas streamtemperature and flow rate, and rate of perfluoroalkane(s) injection, maybe controlled to achieve the desired concentration of perfluoroalkane(s)to be treated. The resulting gas stream containing theperflouoroalkane(s) is then contacted with the catalyst compositionsdescribed herein.

It should also be noted that after the gas stream has been treated inaccordance with the present invention, further treatment, if desired,may be necessary to remove hydrofluoric acid (formed during thedecomposition of the perfluoroalkanes in the presence of an oxidizingagent and water) from the effluent stream. If the concentration ofhydrofluoric acid in the effluent stream is deemed unacceptable,conventional collection or abatement processes, such as causticscrubbing, may be employed to avoid venting acid gases directly into theatmosphere.

In the more preferred embodiments of the present invention, a relativelysmall percentage, such as about 0.01 to 5% of a base or noble metal,appear to aid the complete conversion of carbon monoxide to carbondioxide in the reaction products. In this connection it has not beenobserved that noble metals perform better than base metals.

Under certain operating conditions, aluminum oxide alone may not possessthe required useful life and may degrade faster than desirablewarranting replacement of the catalyst following a short period ofoperation. However, the aluminum oxide may be used to treat processstreams containing low to moderate concentrations of perfluoroalkanesusing a fluidized bed reactor configuration employing aluminum oxideparticles of a fluidizable size. Using this reactor configuration wouldallow for removing catalyst from the reactor during process operationwhile simultaneously adding fresh catalyst in order to maintain asatisfactory threshold activity of the reactor over a sustained usefulperiod.

The compositions of the catalysts recited herein are stated in percentby weight unless otherwise indicated and were calculated based upon theelements described. When the metal component or components were added bywet impregnation techniques, the weight percent of the metalcomponent(s) were calculated from the concentration of metal(s) withinthe impregnation solution and the amount of impregnation solution usedto prepare the catalyst. When the metal component or components wereadded to the aluminum oxide precursor (e.g. pseudoboehmite) slurried inwater, the weight percent of the metal component(s) were calculated fromthe amount of aluminum oxide precursor and the amount of metal(s)present within the slurry, and the weight loss upon ignition of thealuminum oxide precursor (e.g. 20-30% for pseudoboehmite).

The concentration of CO, CO₂ and perfluoroalkane in the reactor effluentin the following examples described herein were determined using gaschromatographic techniques employing packed columns and both thermalconductivity and flame ionization detectors. The above analyticaltechniques are well known to those skilled in the art.

The additional components added to the aluminum oxide catalyst appear toimprove the effective useful life of the aluminum oxide catalyst bymaintaining the reactivity of the aluminum oxide at a high level forgreater periods of time. This may be referred to as a stabilizingeffect.

In view of the above description and the examples of the processaccording to the present invention which follow, it should be understoodby those skilled in the art that the present invention providesprocesses and catalyst compositions which very effectively transformperfluoroalkanes.

EXAMPLE I

Aluminum oxide was prepared by first adding approximately 1.0 liter ofdistilled, deionized water to a 3.5 liter jar and stirring with alaboratory scale mixer. 500 g of pseudoboehmite alumina was slowly addedto the water while stirring. The pH of the slurry was adjusted toapproximately 3.3 using nitric acid, and the slurry was allowed to stirovernight. In the morning, the slurry was covered and allowed to age forthree days. Following aging, the slurry was mixed for approximately onehour using the laboratory scale mixer, then poured into a drying pan.The drying pan containing the slurry was placed into an oven and heatedto between 100 and 125° C. until dry. Following drying, the resultingsolids were calcined at 535° C.

Following calcination, the above material was crushed and sieved to40/60 mesh granules. 3.0 g (7.5 cm³) of catalyst were loaded into a 1.0cm o.d. stainless steel reactor and heated to 750° C. The catalyst wasthen exposed to 500 ppm hexafluoroethane (C₂F₆) in humid air (2.1 volumepercent water) at a gas hourly spaced velocity of 1,440 hr⁻¹. Thereactor temperature was decreased at approximately 80° C./hr, and theeffluent stream was sampled for the concentration of CO₂ and C₂F₆ atdiscrete periods of time. The conversion of C₂F₆ as a function oftemperature is reported below:

Temperature, ° C. Conversion, % 720 99.5 667 93.1 634 74.3 589 30.5 55211.7 511 3.0

EXAMPLE II

The catalyst prepared to according to Example I was evaluated forstability by exposing 2.4 g (6.0 cm³) of 12-20 mesh catalyst to a gasstream containing 500 ppm C₂F₆, 2.8 volume percent water with thebalance air at a gas hourly space velocity of 1,800 h⁻¹ at 700° C. Theconversion of C₂F₆ decreased from 95% to less than 90% in 18.5 hours andless than 80% in 32.5 hours and less than 60% upon termination of therun (52.5 hours).

EXAMPLE III

The catalyst prepared according to Example I was evaluated for stabilityby exposing 1.0 g (2.5 cm³) of 40/60 mesh catalyst to a gas streamcontaining 1,000 ppm C₂F₆, 3.6 volume percent water with the balance airat a gas hourly space velocity of 4,320 hr⁻¹ at 800° C. The conversionof C₂F₆ remained greater than 99.5% for approximately 12 hours, afterwhich, the conversion of C₂F₆ decreased to approximately 95% in 19.5hours, and to approximately 88% upon termination of the run (24.5hours).

Results presented in Examples I, II and III demonstrate that while thealuminum oxide catalyst is able to achieve greater than 90% destructionof C₂F₆, the conversion of C₂F₆ rapidly decreases with increasingexposure time.

EXAMPLE IV

A magnesium-aluminum oxide catalyst composition was prepared by firstadding approximately 1.5 liters of distilled, deionized water to a 3.5liter jar and stirring with a laboratory scale mixer. 1,000 g ofpseudoboehmite alumina was slowly added to the water while stirring. ThePh of the slurry was adjusted to approximately 3.3 using nitric acid. Tothe slurry was then added approximately 50 g magnesium nitrate and anadditional 250 ml of distilled, deionized water. The slurry was allowedto stir for approximately one hour, and an additional 24.6 g magnesiumnitrate plus 150 ml distilled, deionized water was added to the slurry.The slurry was then allowed to stir overnight. In the morning, theslurry was covered and allowed to age for three days. Following aging,the slurry was mixed for approximately one hour using a laboratory scalemixer, then poured into a drying pan. The drying pan containing theslurry was placed into an oven and heated to between 110° C. and 125° C.until dry. Following drying, the resulting solids were calcined at 535°C. The resulting material was approximately 0.85% by weight magnesium.

Following calcination, the above material was crushed and sieved to40/60 mesh granules. 3.0 g (6.0 cm³) of catalyst were loaded into a 1.0cm o.d. reactor and heated to 500° C. The catalyst was then exposed to500 ppm hexafluoroethane (C₂F₆) in humid air (2.1 volume percent water)at a gas hourly space velocity of 1,800 hr⁻³. The reactor temperaturewas increased at approximately 80° C./hr, and the effluent stream wassampled for the concentration of CO₂ and C2F₆ at discrete periods oftime. The conversion of C₂F₆ as a function of temperature is reportedbelow:

Temperature, ° C. Conversion, % 720 99.5 690 96.7 655 83.9 614 51.6 57516.5 523 5.3

EXAMPLE V

A lanthanum-aluminum oxide composition was prepared by first addingapproximately 1.5 liters of distilled, deionized water to a 3.5 literjar and stirring with a laboratory scale mixer. 1000 g of pseudoboehmitealumina was slowly added to the water while stirring. The pH of theslurry was adjusted to approximately 3.3 using nitric acid. To theslurry was then added approximately 21 g lanthanum nitrate hydrate. Theslurry was then allowed to stir overnight. In the morning, the slurrywas covered and allowed to age for three days. Following aging, theslurry was mixed for approximately one hour using a laboratory scalemixer, then poured into a drying pan. The drying pan containing theslurry was placed into an oven and heated to between 110° C. and 1250°C. until dry. Following drying, the resulting solids were calcined at535° C. The resulting material was approximately 1.0% by weightlanthanum.

Following calcination, the above material was crushed and sieved to40/60 mesh granules. 3.0 g (6.0 cm³) of the catalyst composition wereloaded into a 1.0 cm o.d. reactor and heated to 500° C. The catalyst wasthen exposed to 500 ppm hexafluoroethane (C₂F₆) in humid air (2.1 volumepercent water) at a gas hourly space velocity of 1,800 hr⁻¹. The reactortemperature was increased at approximately 80° C./hr, and the effluentstream was sampled for the concentration of CO₂ and C₂F₆ at discreteperiods of time. The conversion of C₂F₆ as a function of temperature isreported below:

Temperature, ° C. Conversion, % 704 91.2 679 83.0 652 67.3 621 43.4 58822.2 517 2.6

EXAMPLE VI

A chromium-aluminum oxide catalyst composition was prepared by firstadding approximately 1.5 liters of distilled, deionized water to a 3.5liter jar and stirring with a laboratory scale mixer. 1,000 g ofpseudoboehmite alumina was slowly added to the water while stirring. ThepH of the slurry was adjusted to approximately 3.3 using nitric acid. Tothe slurry was then added approximately 44.7 g chromium nitrate hydrate.The slurry was then allowed to stir overnight. In the morning, theslurry was covered and allowed to age for three days. Following aging,the slurry was mixed for approximately one hour using a laboratory scalemixer, then poured into a drying pan. The drying pan containing theslurry was placed into an oven and heated to between 110 and 125° C.until dry. Following drying, the resulting solids were calcined at 535°C. The resulting material was approximately 0.8 wt % chromium.

Following calcination, the above material was crushed and sieved to 6/10mesh granules. 26.5 g(50 cm³) catalyst were loaded into a 2.5 cm o.d.reactor and heated to 450° C. The catalyst was then exposed to 500 ppmhexafluoroethane (C₂F₆) in humid air (2.1 volume percent water) at a gashourly space velocity of 1,800 hr⁻¹. The reactor temperature wasincreased at approximately 100° C./hr, and the effluent stream wassampled for the concentration of CO₂ and C₂F₆ at discrete periods oftime. The conversion of C₂F₆ as a function of temperature is reportedbelow:

Temperature, ° C. Conversion, % 752 99.5 704 95.8 653 82.3 602 58.0 55019.1 500 6.4

EXAMPLE VII

The catalyst prepared according to Example VI was evaluated forstability by exposing 26.5 g (50 cm³) of 6/10 mesh catalyst particles toa gas stream containing 500 ppm C₂F₆, 2.1 volume percent water with thebalance air at a gas hourly space velocity of 1,800 hr⁻¹ at 700° C. Theeffluent stream was sampled for the concentration of CO₂ and C₂F₆ every45 minutes throughout the 19 hour run. The conversion of C₂F₆ remainedconstant at 94.1±0.32% throughout the duration of the run.

Results presented in Example VII demonstrate that the addition ofchromium to the aluminum oxide improves the stability or life of thecatalyst.

EXAMPLE VIII

A cobalt-aluminum oxide was prepared by impregnating to incipientwetness 7.10 g of 12/20 mesh aluminum oxide prepared according toExample I with an aqueous solution containing 3.4 wt % cobalt. Thesolution was prepared by dissolving 3.0 g cobalt acetate and 3.0 gtriethanolamine in 15 ml distilled, deionized water. Followingimpregnation, the material was dried at 120° C. followed by calcining at450° C. The resulting material was 4.0 wt % cobalt.

EXAMPLE IX

The catalyst prepared according to Example VIII was evaluated forstability by exposing 1.0 g (2.0 cm³) of 12/20 mesh catalyst particlesto a gas stream containing 1,000 ppm C₂F₆, 2.7 volume percent water withthe balance air at a gas hourly space velocity of 6,000 hr⁻¹ at 800° C.for 43 hours. The effluent stream was sampled every hour for CO₂ andC₂F₆. The conversion of C₂F₆ remained constant at 89.6±0.10% throughoutthe remainder of the run.

Results presented in Example IX demonstrate that the addition of cobaltto the aluminum oxide improves the stability of the catalyst.

EXAMPLE X

A cerium-aluminum oxide catalyst was prepared by first addingapproximately 1.5 liters of distilled, deionized water to a 3.5 literjar and stirring with a laboratory scale mixer. 650 g of pseudoboehmitealumina was slowly added to the water while stirring. The pH of theslurry was adjusted to approximately 3.3 using nitric acid. To theslurry was then added approximately 70 g cerium nitrate hydrate. Theslurry was then allowed to stir overnight. In the morning, the slurrywas covered and allowed to age for 32 hours. Following aging, a 35 gportion of slurry was removed and dried at 125° C. Following drying, theresulting solids were calcined by heating to 535° C. at 7° C./min andmaintaining this temperature for 2 hours, then heating to 900° C. at 5°C./min and maintaining this temperature for 1 hour. The resultingmaterial was approximately 5.0% by weight cerium.

Following calcination, the above material was crushed and sieved to40/60 mesh granules. 3.0 g (6.0 cm³) catalyst were loaded into a 1.0 cmo.d. reactor and heated to 575° C. The catalyst was then exposed to 500ppm hexafluoroethane (C₂F₆) in humid air (2.1 volume percent water) at agas hourly space velocity of 1,800 hr⁻¹. The reactor temperature wasincreased at approximately 80° C./hr, and the effluent stream wassampled for the concentration of CO₂ and C₂F₆ at discrete periods oftime. The conversion of C₂F₆ as a function of temperature is reportedbelow:

Temperature, ° C. Conversion, % 749 99.5 699 90.0 660 72.3 609 37.2 5757.7

EXAMPLE XI

The catalyst prepared according to Example X was evaluated for stabilityby exposing 1.0 g (2.5 cm³) of 40/60 mesh catalyst particles to a gasstream containing 500 ppm C₂F₆, 2.1 volume percent water with thebalance air at a gas hourly space velocity of 1,550 hr⁻¹ at 700° C. Theeffluent stream was sampled every hour for CO₂ and C₂F₆. Throughout the17.5 hour duration of the test, the conversion of C₂F₆ remained constantat about 69.01±0.16%.

EXAMPLE XII

The cerium-aluminum oxide slurry prepared according to Example X wascoated onto a monolithic substrate by dipping four 5×5×5 cm piece ofsubstrate with a cell density of 62 channel/cm² into the slurry. Thechannels were cleared of excess slurry by blowing air through thechannels using an air knife. The pieces of monolith were then dried andcalcined at 535° C. for 2 hours. Once calcined, the coating procedurewas repeated, and the final material was again dried and calcined at535° C. for 2 hours. The catalyst loading following calcination wasapproximately 110 g/liter of monolith.

Following calcination, 2.5 cm diameter cores of monolith were cut fromthe blocks using a core saw. Two cores were loaded into a 2.5 cmdiameter stainless steel reactor and heated to 550° C. in flowing, humidair. The catalyst was then exposed to 500 ppm hexafluoroethane (C₂F₆) inhumid air (2.1 volume percent water) at a gas hourly space velocity of1,800 hr⁻¹. The reactor temperature was increased at approximately 100°C./hr, and the effluent stream was sampled for the concentration of CO₂and C₂F₆ at discrete periods of time. The conversion of C₂F₆ as afunction of temperature is reported below:

Temperature, ° C. Conversion, % 805 93.2 745 65.3 698 48.7 650 28.4 60110.2 555 1.2

Results reported above demonstrate that the catalyst can be coated ontoa monolith and used to transform perfluoroalkanes.

EXAMPLE XIII

A zirconium-aluminum oxide catalyst was prepared by first addingapproximately 1.5 liters of distilled, deionized water to a 3.5 literjar and stirring with a laboratory scale mixer. 750 g of pseudoboehmitealumina was slowly added to the water while stirring. The pH of theslurry was adjusted to approximately 3.3 using nitric acid.Approximately 750 g of zirconium hydroxide was then added to the slurryand the pH of the slurry was adjusted to approximately 3.3 using nitricacid. The slurry was then allowed to stir overnight. In the morning, theslurry was covered and allowed to age for three days. Following aging,approximately 50 g of slurry was removed and dried at 125° C. Followingdrying, the resulting solids were calcined by heating to 535° C. at 7°C./min and maintaining this temperature for 2 hours, then heating to900° C. at 5° C./min and maintaining this temperature for 1 hour. Theresulting composition contained approximately 50%. by weight zirconiumoxide.

Following calcination, the above material was crushed and sieved to40/60 mesh granules, 3.0 g(6.0 cm³) catalyst were loaded into a 1.0 cmo.d. reactor and heated to 550° C. The catalyst was then exposed to 500ppm hexafluoroethane (C₂F₆) in humid air (2.1 volume percent water) at agas hourly space velocity of 1,800 hr⁻¹. The reactor temperature wasincreased at approximately 80° C./hr, and then the effluent stream wassampled for the concentration of C₂ and C₂F₆ at discrete period of time.The conversion of C₂F₆ as a function of temperature is reported below:

Temperature, ° C. Conversion, % 800 99.5 746 84.5 694 50.7 655 31.6 61111.5 550 0.4

EXAMPLE XIV

A zirconium-aluminum oxide catalyst was prepared by first addingapproximately 1.5 liters of distilled, deionized water to a 3.5 literjar and stirring with a laboratory scale mixer. 1.0 kg of pseudoboehmitealumina was slowly added to the water while stirring. To the slurry wasadded 105 g of a zirconium oxynitrate (20% zirconia) solution. The Ph ofthe slurry was adjusted to approximately 3.3 using nitric acid. Theslurry was then allowed to stir overnight. In the morning, the slurrywas covered and allowed to age for three days. Following aging, theslurry was removed and dried at 125° C. Following drying, the resultingsolids were calcined by heating to 535° C. at 7° C./min and maintainingthis temperature for 2 hours. The resulting material was approximately3% by weight zirconium oxide.

Following calcination, the above material was crushed and sieved to10/18 mesh granules. 28.2 g (50 cm³) catalyst were loaded into a 1.0 cmo.d. reactor and heated to 520° C. The catalyst was then exposed to 500ppm hexafluoroethane (C₂F₆) in humid air (2.1 volume percent water) at agas hourly space velocity of 1,800 hr⁻¹. The reactor temperature wasincreased at approximately 100° C./hr, and the effluent stream wassampled for the concentration of CO₂ and C₂F₆ at discrete periods oftime. The conversion of C₂F₆ as a function of temperature is reportedbelow:

Temperature, ° C. Conversion, % 700 99.5 649 88.8 594 61.4 542 23.2 52012.9

EXAMPLE XV

The catalyst prepared according to Example XIV was evaluated forstability by exposing 69 g (120 cm³) of 6/10 mesh catalyst particles toa gas stream containing 500 ppm C₂F₆, 2.1 volume percent water with thebalance air at a gas hourly space velocity of 1,800 hr⁻¹ at 700° C. Theeffluent stream was sampled every hour for CO₂ and C₂F₆. CO₂ was theonly carbon-containing reaction product detected in the reactor effluentstream. The conversion of C₂F₆ increased from 90 to 95% during the first20 hours of the run, and remained greater than 90% for approximately 340hours of reaction exposure. Following 340 hours, the conversion of C₂F₆decreased to less than 90%.

EXAMPLE XVI

A more preferred catalyst was prepared by impregnating to incipientwetness 200 g of 6/12 mesh of the 3% zirconia-alumina catalyst preparedaccording to Example XIV using an aqueous solution containing 4.3 wt %cobalt. The solution was prepared by dissolving 80.0 g cobalt acetateand 60.0 g triethanolamine in 300 ml distilled, deionized water.Following impregnation, the material was dried at 120° C., then calcinedat 450° C. The resulting material was 5.0 wt %

EXAMPLE XVII

The catalyst prepared according to Example XVI was evaluated forstability by exposing 90 g (150 cm³) of 6/12 mesh catalyst particles toa gas stream containing 500 ppm C₂F₆, 3.2 volume percent water with thebalance air at a gas hourly space velocity of 1,800 hr⁻¹ at 700° C. Theeffluent stream was sampled every hour for CO₂ and C₂F₆. CO₂ was theonly carbon-containing reaction product detected in the reactor effluentstream. The conversion of C₂F₆ increased from 88 to 98% during the first25 hours of the run, then remained constant at 98% throughout theduration of the 400 hour run.

EXAMPLE XVIII

The catalyst prepared according to Example XVI was evaluated forstability by exposing 1.0 g (1.8 cm³) of 40/60 mesh catalyst particlesto a gas stream containing 1000 ppm C₂F₆, 3.6 volume percent water withthe balance air at a gas hourly space velocity of 6,000 hr⁻¹ at 800° C.The effluent stream was sampled every hour for CO₂ and C₂F₆. CO₂ was theonly carbon-containing reaction product detected in the reactor effluentstream. The conversion of C₂F₆ increased from 90 to 95% during the first7 hours of reaction exposure. The conversion of C₂F₆ remained greaterthan 90% throughout the duration of the 78 hour run.

EXAMPLE XIX

The catalyst prepared according to Example XIV was crushed and sieved to12/20 mesh, then exposed to 5,000 ppm tetrafluoromethan (CF₄) in humidair (2.7 volume percent water) at a gas hourly space velocity of 2,000hr⁻¹ at 750° C. The reactor temperature was decreased at approximately70° C./hr, and the effluent stream was sampled for the concentration ofCO₂ and CF₄ at discrete periods of time. The conversion of CF₄ as afunction of temperature is reported below:

Temperature, ° C. Conversion, % 750 97.4 700 65.8 650 34.2 600 10.5

In view of the foregoing description and examples, it should be readilyappreciated that aluminum oxide represents an effective catalyst for thetransformation of perfluoroalkanes and that its effective useful lifecan be expanded by the addition of one or more of the additionalcomponents described herein in a process according to the presentinvention.

What is claimed is:
 1. A process for the destruction ofperfluoroalkanes, the process comprising contacting a gas stream and acatalyst; wherein: the gas stream comprises water and one or moreperfluoroalkanes; the catalyst comprises aluminum oxide; and thecontacting step is performed at a temperature and gas hourly spacevelocity sufficient to reduce the concentration of the perfluoroalkanesin the gas stream.
 2. The process of claim 1, wherein the aluminum oxideis gamma phase, delta phase, kappa phase, theta phase, or mixturesthereof.
 3. The process of claim 1, wherein: the catalyst furthercomprises zirconium; and the catalyst is from about 0.01 weight % toabout 50 weight % ZrO₂.
 4. The process of claim 1 wherein: the catalystfurther comprises cobalt; and the catalyst is from about 0.01 weight %to about 50 weight % cobalt.
 5. The process of claim 1 wherein thecatalyst further comprises: from about 0.01 weight % to about 50 weight% ZrO₂; and from about 0.01 weight % to about 50 weight % cobalt,wherein the aluminum oxide is present at about at least 50 weight %. 6.The process of claim 1, 2, 3, 4, or 5 wherein the catalyst furthercomprises about 0.01 weight % to about 5 weight % of a base metal. 7.The process of claim 1, 2, 3, 4 or 5 wherein the catalyst furthercomprises about 0.01 weight % to about 5 weight % of a noble metal. 8.The process of claim 1, 2, 3, 4 or 5, wherein the gas stream and thecatalyst are contacted at a temperature of about 400° C. to about 1000°C.
 9. The process of claim 7, wherein the temperature is about 500° C.to about 800° C.
 10. The process of claim 8, wherein the temperature isabout 500° C. to about 800° C.
 11. The process of claim 1, wherein thegas stream further comprises an oxidizing agent.
 12. The process ofclaim 1, 2, 3, 4 or 5, wherein the catalyst is coated on an inertcarrier.
 13. The process of claim 1, wherein the perfluoroalkanecomprises CF₄, C₂F₆, C₃F₈, C₄F₈, or C₄F₁₀.
 14. The process of claim 1,wherein the gas hourly space velocity is about 500 hour⁻¹ to about300,000 hour⁻¹.
 15. The process of claim 1, wherein the gas hourly spacevelocity is about 1000 hour⁻¹ to about 20,000 hour⁻¹.
 16. The process ofclaim 1, wherein the contacting step reduces the concentration ofperfluoroalkanes in the gas stream at least 80%.
 17. The process ofclaim 1, wherein the contacting step reduces the concentration ofperfluoroalkanes in the gas stream by at least 90%.
 18. The process ofclaim 1, wherein the gas stream further comprises oxygen.
 19. Theprocess of claim 1, wherein the catalyst is present in the form of apellet, granule, ring, sphere, or cylinder.
 20. The process of claim 1,wherein the catalyst consists essentially of gamma phase aluminum oxide,zirconium oxide, cobalt, and a noble metal.